Rhythmical Pulsation in Scyphomedusae

Rhythmical Pulsation in Scyphomedusae

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Rhythmical Pulsation in Scyphomedusae

Rhythmical Pulsation in Scyphomedusae

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Excerpt

If we cut off the marginal sense-organs of the scyphomedusa Cassiopea, the disk* becomes paralyzed and does not pulsate in seawater. The disk will pulsate in sea-water, however, if we make either a single ring or a series of concentric broken-ring-like cuts through the muscular tissue of the sub-umbrella. Then upon momentarily stimulating the disk in any manner, it suddenly springs into rapid, rhythmical pulsation so regular and sustained as to recall the movement of clockwork.

Pulsation will not start unless the disk be momentarily stimulated, as by a mechanical or electrical shock or by a single touch with a crystal of K2SO4, but once started it continues indefinitely in normal sea-water without further external stimulation.

The waves of pulsation all arise from the stimulated point, and the labyrinth of sub-umbrella tissue around this center must form a closed circuit. It is not necessary that the cuts through the sub-umbrella tissue of the disk be concentric circles, for any shape will pulsate which allows contraction waves to travel through tissue forming a closed circuit from the stimulated center and back to this center. When each wave returns to the center it is reinforced and again sent out through the circuit; and thus the center sustains the pulsation.

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